This application is based upon and claims benefit of priority of Japanese Patent Application No. 2001-343138 filed on Nov. 8, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a voltage regulator for controlling an output of an alternator for use in an automotive vehicle, and more particularly to a voltage regulator that controls an output of an alternator a driving torque of which is controlled.
2. Description of Related Art
An example of a voltage regulator that controls an output of an alternator to various levels without changing the alternator itself is disclosed in JP-A-5-316667. In this voltage regulator, a circuit for restricting excitation current of the alternator is included, and the output of the alternator is changed by function-trimming of divider resistors in the restricting circuit.
In a recent automotive vehicle, a higher alternator output is required to supply electrical power to various electrical and electronic components. On the other hand, it is required to stabilize rotational speed of an engine, especially in its idling state. The rotational speed of the engine is considerably influenced by a driving torque of the alternator when an alternator generating a high power is used. Therefore, the engine has to be controlled taking the driving torque of the alternator into consideration. The driving torque may be calculated based on an amount of excitation current supplied to a field winding of the alternator.
A voltage regulator constituted by a monolithic IC (integrated circuit) is becoming widely used in order to make the voltage regulator compact. To calculate the rotational torque of an alternator based on the excitation current, it is necessary to precisely detect the amount of the excitation current. Because the excitation current is detected by a sensing resistor in the voltage regulator, a resistance of the sensing resistor has to be precisely set. The resistance of the sensing resistor is set to a desired level by function-trimming the resistor. However, it is difficult to precisely set the resistance because an amount of current for setting the resistance is restricted by a size of a probing needle to a much lower level than an amount of current in an actual use. In addition, it is also difficult to precisely set an amplification factor of an amplifier for amplifying a voltage sensed by the sensing resistor.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide a voltage regulator in which an amount of excitation current of an alternator is correctly detected without precisely setting the resistance of a sensing resistor by function-trimming or the like.
The alternator is composed of a stator having an armature winding, a rotor having a field winding and a rectifier for rectifying an alternating current generated in the armature winding to an direct current. A voltage regulator for controlling an output of the alternator is connected to the alternator. The alternator output is controlled by controlling an amount of an excitation current supplied to the field winding.
The voltage regulator includes a sensing resistor through which a current proportional to an amount of the excitation current flows. A voltage sensed by the sensing resistor is amplified by an amplifier outputting a detected voltage. The detected voltage is compared with a reference voltage that correctly corresponds to the amount of the excitation current. An amplification factor of the amplifier is adjusted based on a difference between the detected voltage and the reference voltage thereby to equalize the detected voltage to the reference voltage. In this manner, the amount of the excitation current is precisely detected without adjusting a resistance of the sensing resistor by function-trimming or the like.
Data indicating the difference between the detected voltage and the reference voltage are stored in a non-volatile memory, and the amplification factor of the amplifier is adjusted based on the data stored in the non-volatile memory. That is, the amount of the excitation current is precisely detected by electronically adjusting the detected voltage without mechanically trimming the sensing resistor. In addition, a desired amount of the excitation current is set by an electronic control unit that determines the amount of the excitation current, taking a rotational torque required for driving the alternator into consideration to stabilize an idling speed of the engine.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.